The bottom triangle is a 30°-60°-90° triangle that has the special property that its hypotenuse is twice the length of the shortest leg, 20√3.
The upper triangle is a 45°-45°-90° triangle, in which the hypotenuse is longer than one of its legs by a factor of √2.
All this to say x = √2 × 20√3 = 20√6 (A).